Power transmission

ABSTRACT

A displacement adjusting system for a variable displacement pump utilizes a pair of bleed circuits connected as a hydraulic bridge to control the servomotor of the pump so as to maintain a balance between the pressure levels generated in the command bleed circuit and in the feedback bleed circuit. The adjustable restriction in the feedback circuit is of the laminar flow type, its length being adjusted with changes in pump displacement. Input torque is limited by a relief valve acting on the control pressure in the command circuit. Pump outlet pressure is limited by a valve which disables the bleed circuits. The system is applicable to both one-way and reversible displacement pumps.

States Patent [1 1 Write iEreeden Sept. 11, 1973 1 i POWER TRANSMISSIONRobert H. Breeden, Metamora, Mich.

[221 Filed: Sept. 22, 1971 [21] Appl. No.: 182,677

[75] Inventor:

Primary ExaminerWilliam L. Freeh Assistant ExaminerGregory LaPointeAtt0meyTheodore Van Meter [57] ABSTRACT A displacement adjusting systemfor a variable displacement pump utilizes a pair of bleed circuitsconnected as a hydraulic bridge to control the servomotor of the pump soas to maintain a balance between the pressure levels generated in thecommand bleed circuit and in the feedback bleed circuit. The adjustablerestriction in the feedback circuit is of the laminar flow type, itslength being adjusted with changes in pump displacement. Input torque islimited by a relief valve acting on the control pressure in the commandcircuit. Pump outlet pressure is limited by a valve which disables thebleed circuits. The system is applicable to both one-way and reversibledisplacement pumps.

10 Claims, 2 Drawing Figures PAIENTEnsm 1m:

SHEET 1 BF 2 ATTO RNEY POWER TRANSMISSION ln hydraulic powertransmission systems utilizing a variable displacement pump with ahydraulic servomotor for operating the displacement varying member ofthe pump, it has been proposed frequently to utilize a hydraulic bridgecircuit for controlling theservomotor. Such a circuit by its analogy tothe electrical Wheatstone bridge, utilizes a pair of bleed circuitsgenerating intermediate pressures, one of which may be adjusted bycommand and the other which is adjusted by the servomotor response.Examples of such controls appear in the U.S. Pat. to Doc, No. 2,177,098,Oct. 24,1939, and U.S. Pat. to Tweedale, No. 2,253,663, Aug. 26, 1941.The former uses adjustable spring loaded relief valves in the respectivebleed circuits for setting the intermediate pressure levels and thelatter utilizes compensated flow control valves for the same purpose. Ineach case, the appropriate pressure drops in the bleed circuits areestablished by orifices in which turbulent flow takes place. Pressuredropping restrictions of the laminar flow type have been proposed forcontrolling variable displacement pumps as in the U.S. Pat. to Waldie,No. 2,4l8,532, Apr. 8, 1947 (FIG. 5)'and'U.S. Pat. to Lonnemo, No.3,554,093, Jan. 12, 1971. In Waldie the pump is regulated to maintain asubstantially constant, but adjustable outlet pressure. The laminar flowrestriction is merely ancillary to this function in that it provides ameans for adjusting the outlet pressure. In Lonnemo the laminar flowrestriction is one of three influences upon the displacement adjustingmember, the other two being the pump outlet pressure and a spring. Theseinfluences result in maintaining the pump at full, displacement exceptwhen the load requires more than a predetermined input torque at thepump shaft. The control then maintains the displacement at the highestlevel that will requirethis maximum input torque.

The present invention is based upon the discovery that a single laminarflow restriction may be so constructed and connected that it willgenerate the feedback control pressure in a hydraulic bridge circuit asa substitute for the usual fixed and variable turbulent flow orifices toproduce the same local or remote conferred to withconstant speed pumpsto maintain a limit able to change the pump displacement, hydraulicservomotor means to shift the member, a source of control pressurefluid, oppositely acting means for controlling the servomotor includinga pair of bleed circuits extending from the fluid pressure source, onebleed circuit constituting the command circuit and having restrictingmeans for generating a controlling pressure at any commanded level, theother bleed circuit constituting a feedback circuit and havinglaminar-flow restrictions of variable length connected to the shiftablemember for generating an opposing controlling pressure at a levelresponsive to the position of the shiftable member whereby the pumpdisplacement may be adjusted by changing the degree of restriction inthe command circuit.

IN THE DRAWINGS FIG. 1 is a circuit diagram of a first form ,of thepresent invention.

FIG. 2 is a circuit diagram of a second form of the present invention.

- Referring now to FIG. 1, a one-way variable displacement pump 10 hasan inlet 12 and an outlet 14. A member 16 for adjusting the pumpdisplacement is under the control of a servomotor indicated by thepiston '18.

springs 28 and 30 and may be shifted to either side of center by pilotservomotor 32 and 34. These pilot servomotors are connected to respondto the intermediate control pressures generated in the bleed-circuits ofthe hydraulic bridge control.

The command bleed circuit consists of the fixed re- I strictor and thevariable restrictor 38, connected in series between a source of pressurefluid, represented by the branch line 24, and the reservoir. Thefeedback bleed circuit comprises the branch 40, leading from the samepressure fluid source '24, to a variable restrictor of the laminar flowtype indicated generally at 42 and after passing through thisrestrictor,-e xtends by the line 44 to the reservoir. The laminar flowrestrictor 432 comon'the horsepower required toldrivethe pump. Such acontrol system will function, moreover, at any desired torque-levelmerely by a simple spring adjustmentwithout requiring change orsubstitution of any of. the mechanical parts such as cams, springs, orthe like. It is frequently desirable to provide for both manual andautomatic adjustment of pump or motor displacement with remote controlcapability. Other common requirements include automatic pressure limits,automatic displacement limits and coordinated pump and motor controlsfor vehicle propulsion drive.

It is an object of the present invention, therefore, to provide animproved displacement adjusting system for a variable displacement pumpto take advantage of the unique characteristics of laminar flowrestrictions to improve the performance capabilities of such systems,

and to do so with simple reliable, lowcost components. This the presentinvention achieves through providing a displacement adjusting system fora variable displacement pump which comprises a member shiftprises' acylinder '46 within which is a freely slidable, somewhat loose fittingplunger 48. Agroove 50 in the cylinder wall provides a tap-off point atwhich control pressures are generated and which'isconnected by a line 52to the pilot servomotor 34'. Similarly, a line 54 connects the pilotservomotor-32 to a point intermedi-' ate the restrictors 36and 38. Theplunger .48 is mechanically connected, as indicated by the dash anddouble dot line 56, with the displacement varying member 16 of the pump10. This connection maytake any of the many known forms. For example, inU.S. Pat. to

l the connection should be such that as the servomotor ablefeedbackconnections between a pump stroking meniberand a feedback valvecontrol are illustrated in U.S. Pat. tdDoe No. 2,177,098 at 42,56, 54 ofFIG. 1 and in U.S. Pat. to Keel No. 2,870,746, FIGS. 3 and 4 at 118,112, 114, and 110. It will be understood that 18 moves to decrease thepump displacement, the plunger 48 will be moved to decrease theresistance between lines 40 and 52 and simultaneously increase thatbetween lines 52 and 44.

In order to take advantage of the capabilities of the laminar flowfeedback circuit for the purpose of adjustably limiting the input torquerequired at the pump 10, the simple pressure responsive relief valve 58is connected to the branch line 54 so as to limit the maximum pressurewhich can be generated for command purposes and applied to theservomotor 32. This pressure may be adjusted by adjusting the spring 60.For prime movers which maintain substantially constant speed over a widetorque range, such a control will maintain a constant horsepower limit,maintaining a substantially hyperbolic relationship between pump outputflow and output pressure. Similarly, in order to provide a maximum limitto the pressure in the pump outlet line 14, a pressure responsivetwo-way valve 62 may be connected into the line 64 between pilot valve22 and servomotor 18. The pressure limiting valve 62 is con nected byline 66 and line 24 to the pump outlet line 14, and when pressuretherein reaches a predetermined high value, valve 62 shifts, cutting offservomotor 18 from pilot valve 22 and connecting it directly to branch66. This forces the pump to a new displacement position sufficientlysmall to avoid further pressure buildup in the outlet line 14.

In the operation of the embodiment illustrated in FIG. 1, normally thepump displacement is regulated by action of the pilot valve 22 upon theservomotor 18. Pilot valve 22 achieves a'center position only when thepressures in servomotors 32 and 34 are balanced. Under such conditions,in the command circuit, a continuous bleed takes place from line 24through restrictors 36 and 38 and the intermediate pressure is directedfor control purposes through line 54 to servomotor 32. Likewise, in thefeedback'bleed circuit, flow occurs through line 40 to the laminar flowrestrictor 42 and through it and line 44 to the reservoir. Theintermediate pressure measured at the groove 50 is directed through line52 to servomotor 34. Any change required or desired in the pumpdisplacement setting is produced by changing the degree of restrictionat command restrictor 38, thus causing a new control pres- 54 andservomotor 32. This will causepilot val ve22 to shift, actuatingtheservomotor 18 in the appropriate direction and carrying with it theplunger 48 of the laminar flow restrictor to produce a new controlpressure at groove 50 and line 52 which will again balance servomotor 34against servomotor 32, restoring pilot valve 22 to neutral.

Since in a laminar flow restriction such as 42, the pressure drop frominlet to the control groove 50 is a sure, either higher or lower thanbefore, to exist in line substantially linear function of the distancethrough d which fluid has to flow in the clearance space, and since anymovement of the plunger 48 produces opposite changes in the length ofthe flow paths (8) from the inlet to the groove 50 and (b) from thegroove 50 to the outlet, and since the inlet pressure corresponds to thepressure in the pump outletline, it follows that the control pressure atgroove 50 is a function of the product of pump outlet pressure andpumpdisplacement setting. This product is, in turn, a measure of theinput torque requirements of the pump under these conditions, and it isthis pressure which must be balanced by the pressure in line 54 in orderfor any setting of the servomotor 18 to be maintained fixed.

If the adjustable command restrictor 38 is so operated as to require adisplacement setting which at the particular outlet pressure level beingthen experienced would exceed the allowable input torque of the pump,then the torque limiting relief valve 58 will open, thus permittingpilot valve 22 to shift upwardly in FIG. 1 and direct pump outletpressure to the servomotor 18 and reduce the pump displacement, untilthe desired input torque is not exceeded. The control, furthermore,permits maximum input torque regulation at any desired level withoutchanging parts. Merely by adjusting the spring 60 of the relief valve 58any maximum torque level may be chosen, since the pressure in groove 50and line 52 is always a measure of the product of pump outlet pressureand pump displacement.

For limitation of the maximum operating pressure in outlet line 14,valves 62, which normally maintains communication between pilot valve 22and servomotor 18 will, on a predetermined pressure rise in line 14,disconnect the pilot valve 22 and connect servomotor 18 directly to thepump outlet line 14. The fluid delivered by the pump is thus caused toreduce the pump displacement until a satisfactory pressure level isachieved.

Referring now to FIG. 2, a similar system is there illustrated asapplied to a reversible variable displacement pump having an associatedconstant displacement control pressure pump 102 attached to it. The pump100 delivers either into the line 104 or the line 106 and withdrawsfluid from the other, depending upon its displacement setting. Pump 102delivers into a control pressure supply line 108, the pressure in whichis governed by a relief valve 110. The displacement of the pump 100 isshiftable between maximums on either side'of center through adifferential'area servomotor indicated by the pistons l 12 and 114 ofsmall and large areas respectively. Piston 112 is permanently connectedto the control pressure line 108 which also supplies control pressure tothe three-way pilot valve 1 16. The latter controls the large areaservomotor 114 through a line 118 and has a reservoir return line 120.

The pilot valve 116 is similar to the pilot valve 22 of FIG. 1. However,duplicate hydraulic bridge circuits are provided for controlling pilotvalve 116, each circuit being effective only on'one side of the zerodisplacement position of the pump 100. A pressure fluid supply source tothe bleed circuits is provided by means of line 122. A shuttle valve 124in the position illustrated, supplies fluid through line 126 fromanother shuttle valve 128 which, in the position illustrated, suppliesfluid from the main pump line 106 and in the opposite position, suppliesfluid from the other main line 104. Likewise, shuttle valve 124 suppliesfluid from the control pump 102 through line 108 whenever that pressureis higher than the pressure in either of the pump main lines 104 and106. A bel-erank 130 transmits motion from the displacement varyingmechanism of pump 100 to a dual laminar flow restrictor device 132-134.

The two command bleed circuits are supplied'from the fluid pressuresource by line 136, the lower bleed circuit being constituted by fixedrestrictor 138 and variable restrictor 140 and the upper bleed circuitbeing constituted by the fixed restrictor 142 and the variablerestrictor 144. The intermediate control pressures which are generatedin these command bleed circuits are fed to shuttle valves 146 and 148connected to the pilot servomotors of valve 116.

The feedback bleed circuits pass from the fluid pressure source 122through the laminar flow restrictors 132 and 134 to the outlet lines 137and 139. Intermediate control pressure is tapped off and fed throughlines 141 and 143 to the opposite sides of the shuttle valves 146 and148, the arrangement being such that when, as illustrated commandrestrictor 144 is in control, restrictor 132 provides the feedback andwhen command restrictor 140 is in control, restrictor 134 provides thefeedback and shuttle valves 146 and 148 occupy positions opposite to thepositions illustrated. Alternatively, the command restrictors 140 and144 may be located at 137 and 139 and shuttle valves 146 and 148eliminated.

Limitation of delivery pressure is provided by the pressure responsivevalve 150 connected to respond to the pressure in line 136. Similarly tovalve 62, this valve disconnects the pilot valve 116 from the servomotor114 and instead connects it to a line 152 leading to the main pump line106. If this line happens to be under pressure, that pressure will besupplied to the servomotor 114, reducing the pump displacement deliveredinto line 106. If that line, however,is not under pressure, valve 150will exhaust servomotor 114, thus reducing the pump displacement intoline 104.

If limitation of input toruqe is desired, valves similar to valve 58 ofFIG. 1 may be'connected to dump at a predetermined pressure in the lineahead of restrictors 140 and 144.

In those applications where it is desirable to simultaneously controlbrakes, clutches and the like, a valve 154 may be connected through aline 156 and shuttle valve 158 to receive pressure fluidv from either ofthe lines 141 or 143. When the pressure in both these lines is zero, ashappens in the zero displacement position of pump 100 and of laminarrestrictors 132 and 134, then the spring bias of valve 154 holds it inthe position shown in FIG. 2 to exhaust the brake and clutch lines 160and 162 back to reservoir through line 164. Thus, a brake which isspring applied and hydraulically released and a clutch which is springreleased and hydraulically applied, may be controlled by valve 154either directly or through a hydraulic relay. As soon as placement pumpor motor unit comprising a member trolling the servomotor including apair of bleed circuits extending from the fluid pressure source, onebleed circuit constituting the command circuit and having restrictingmeans for generating a controlling pressure at any commanded level, theother bleed circuit constituting the feedback circuit and having laminarflow restrictions of variable length connected to the shiftable memberfor generating an opposing controlling pressure at a level responsive tothe position of the shiftable member, whereby the unit displacement maybe adjusted by changing the degree of restriction in the commandcircuit.

2. A system as defined in claim 1 wherein the means for controlling theservomotor includes a pilot valve responsive to the opposing pressuresgenerated in the bleed circuits.

3. A system as defined in claim 1 wherein the bleed circuits aresupplied from the high pressure side of the pressure builds up in eitherline 141 or 143, valve 154 will deliver it to lines 160 and 162, thusreleasing the brake and applying the clutch.

The control of the displacement of a hydraulic motor may be accomplishedsimilarly to the manner above described, as for example by using acircuit similar to FIG. 1, although without necessity for providing thepressure limiting valve 62. In this case, however, the connectionbetween the variable laminar flow restrictor plunger 48 and thedisplacement controller of the motor will be reversed.

I claim:

1. A displacement adjusting system for a variable disunit.

4. A system as defined in claim 3 wherein a pressure responsive valve isconnected to limit the pressure level in the command circuit whereby themaximum torque input to the pump may be limited by the combinedvariations in pump outlet pressure and pump displacement as reflected inthe pressure level in the feedback circuit.

5. A system as defined in claim 4 including means for adjusting theaction of the pressure responsive valve whereby to change the inputtorque level to which the pump is limited.

6. A system as defined in claim 1 having means responsive to theachieving of a selected maximum pressure at the pump outlet fordelivering fluid from the pump outlet to the servomotor directly andindependently of the control pressure levelsin the bleed circuit.

7. A system as defined in claim 3 having means responsive to theachieving of a selected maximum pressure at the pump outlet fordelivering fluid from the pump outlet to the servomotor directly andindependently of the control pressure levels in the bleed circuits.

8. A system as defined in claim 1 wherein the pump displacement is bothvariable and reversible across a neutral setting and a second pair ofsimilar bleed circuits are provided to control the servomotor on theopposite side of neutral.

9. A system as defined in claim 8 including a pair-of shuttle valves forcontrolling the action of the respective bleed circuits upon theservomotor.

10. A system as defined in claim 1 wherein the laminar flow restrictionsare mutually variable, an increase in one resulting in a correspondingdecrease in the other.

1. A displacement adjusting system for a variable displacement pump ormotor unit comprising a member shiftable to change the unitdisplacement, hydraulic servomotor means to shift the member, a sourceof control pressure fluid, oppositely acting means for controlling theservomotor including a pair of bleed circuits extending from the fluidpressure source, one bleed circuit constituting the command circuit andhaving restricting means for generating a controlling pressure at anycommanded level, the other bleed circuit constituting the feedbackcircuit and having laminar flow restrictions of variable lengthconnected to the shiftable member for generating an opposing controllingpressure at a level responsive to the position of the shiftable member,whereby the unit displacement may be adjusted by changing the degree ofrestriction in the command circuit.
 2. A system as defined in claim 1wherein the means for controlling the servomotor includes a pilot valveresponsive to the opposing pressures generated in the bleed circuits. 3.A system as defined in claim 1 wherein the bleed circuits are suppliedfrom the high pressure side of the unit.
 4. A system as defined in claim3 wherein a pressure responsive valve is connected to limit the pressurelevel in the command circuit whereby the maximum torque input to thepump may be limited by the combined variations in pump outlet pressureand pump displacement as reflected in the pressure level in the feedbackcircuit.
 5. A system as defined in claim 4 including means for adjustingthe action of the pressure responsive valve whereby to change the inputtorque level to which the pump is limited.
 6. A system as defined inclaim 1 having means responsive to the achieving of a selected maximumpressure at the pump outlet for delivering fluid from the pump outlet tothe servomotor directly and independently of the control pressure levelsin the bleed circuit.
 7. A system as defined in claim 3 having meansresponsive to the achieving of a selected maximum pressure at the pumpoutlet for delivering fluid from the pump outlet to the servomotordirectly and independently of the control pressure levels in the bleedcircuits.
 8. A system as defined in claim 1 wherein the pumpdisplacement is both variable and reversible across a neutral settingand a second pair of similar bleed circuits are provided to control theservomotor on the opposite side of neutral.
 9. A system as defined inclaim 8 including a pair of shuttle valves for controlling the action ofthe respective bleed circuits upon the servomotor.
 10. A system asdefined in claim 1 wherein the laminar flow restrictions are mutuallyvariable, an increase in one resulting in a corresponding decrease inthe other.